The present invention relates to a disk device which provides an improved disk format efficiency when a disk eccentricity occurs.
Data storage devices using various types of media such as optical disks and magnetic tapes are known. Among them, hard disk drives (HDDs) have become popular as storage devices for computers to such an extent that they are one of the storage devices indispensable for today's computers. Further, not limited to computers, their application is widening more and more due to the superior characteristics with the advent of moving picture recording/reproducing devices, car navigation systems, removable memories for digital cameras and so on.
Usually, a HDD has magnetic disks as media. In the manufacturing process, the magnetic disks are fixed around the rotary axis of a spindle motor so that they are driven to rotate by the spindle motor. Due to the manufacture or structure, however, spacing occurs between the rotary axis and the magnetic disks. This spacing causes the magnetic disks to rotate eccentrically since the center of the magnetic disks is deviated from the center of the rotary axis. In addition, if the HDD is mounted in such a portable storage device as mentioned above, a still larger disk eccentricity may occur since the HDD is likely to be given external shocks during use. Servo data to control the position of a read/write head is written to tracks on a magnetic disk on the assumption that the magnetic disk would rotate normally. Thus, if a disk eccentricity occurs in read or write operation, the head sees a larger rotary variation than in normal rotation. This may make it impossible for the magnetic head to accurately locate itself, resulting in increased servo data read errors. Conventionally, to reduce these read errors, the interval between servo data timing-indicating servo sector pulses generated based on servo data is corrected. However, this correction of the servo sector pulse interval makes the disk format regions different along the same track among different servo sectors.
Meanwhile, user data is read/written to/from the magnetic disk by the magnetic head. Usually, user data read/write timing-indicating data sector pulses are generated at equal intervals according to a clock which operates at a fixed frequency. Therefore, the disk format requires a certain margin region in order to absorb the variations. This margin region becomes a format loss.